05, Jun, 2017
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INTRODUCTION TO PHYLUM ECHINODERMATA

INTRODUCTION TO PHYLUM ECHINODERMATA
PHYLUM ECHINODERMATA
  • Jacob Klein (1734) first used the term Echinodermata for sea urchins.
  • Linnaeus in 1758 placed Asterias, Echinus and Holothuria under Mollusca.
  • Lamarck (1801) included these animals in the order Echinoderm of the Class Radiata.
  • In 1847 Leuckart gave phylum rank to the Echinodermata.
  • The Echinoderms are spiny skinned animals.
  • They are exclusively marine animals. They do not show distinct head.
  • They show pentaradial symmetry.
  • They show peculiar water vascular system of coelomic origin.
  • They are coelomate animals with pentaramous radial symmetry, that is the body can be divided into five parts arranged around a central axis, but the larva is bilaterally symmetrical.
  • They have an endoskeleton of calcareous ossicles made from mesoderm, there are also external spines which may be movable or fixed.
  • Respiratory organs are minute gills protruding out from the coelome.
  • There is no definite blood vascular system, it is represented only by lacunar tissue, there are no definite excretory organs.
  • Nervous system forms a ring around the mouth with nerves radiating from it, it is the principal nervous system and is in contact with the ectoderm in addition there is a deeper nervous system lying In the mesoderm.
  • Sexes are usually separate but copulation does not take place. Echinodermata have no parasitic forms.
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